Add screenshot to `SentryFeedbackWidget`

[denrase]

:scroll: Description

Add the option to add a screenshot SentryAttachment to the SentryFeedbackWidget

:bulb: Motivation and Context

Closes to #1593

:green_heart: How did you test it?

Unit tests, example app.

:pencil: Checklist

• [x] I reviewed submitted code
• [x] I added tests to verify changes
• [ ] No new PII added or SDK only sends newly added PII if sendDefaultPii is enabled
• [ ] I updated the docs if needed
• [ ] All tests passing
• [x] No breaking changes